ACPAtmospheric Chemistry and PhysicsACPAtmos. Chem. Phys.1680-7324Copernicus GmbHGöttingen, Germany10.5194/acp-12-3753-2012First detection of tidal behaviour in polar mesospheric water vapour by ground based microwave spectroscopyHallgrenK.1HartoghP.11Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany2404201212837533759This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from http://www.atmos-chem-phys.net/12/3753/2012/acp-12-3753-2012.htmlThe full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/3753/2012/acp-12-3753-2012.pdf

Mesospheric water vapour has been observed above ALOMAR in northern Norway
(69° N 16° E) by our group since 1995 using a 22 GHz ground based
microwave spectrometer.
A new instrument with higher sensitivity, providing a much better time
resolution especially in the upper mesosphere, was installed in May 2008. The
time resolution is high enough to provide observations of daily variations in
the water vapour mixing ratio. We present the first ground based detections of
tidal behaviour in the polar middle atmospheric water vapour distribution.
<br><br>
Diurnal and semidiurnal variations of water vapour have been observed and due
to the long chemical lifetime of water they are assumed to
be caused by changing wind patterns which transport water-rich or poor air
into the
observed region. The detected tidal behaviour does not follow any single other
dynamical field but is instead assumed to be a result of the
different wind components.
<br><br>
Both the diurnal and semidiurnal amplitude and phase components are
resolved. The
former shows a stable seasonal behaviour consistent with
earlier observations of wind fields and model calculations, whereas the latter
appears more complex and no regular behaviour has so far
been observed.